By happy coincidence Comment is free started up shortly after I set out to write my book, The Fallout: How a Guilty Liberal Lost His Innocence. My first reaction to the site's arrival was that its debates vindicated my decision to write the book, insofar as they focused on many of the same issues that were at the core my argument: the political fallout from 9/11, multiculturalism, race, America, Iraq, ideological Islam, crime, and the crisis of liberalism that appeared to be splitting apart the left.

My second reaction was that if I looked at the site for too long I'd never get the book written. But I saw enough before I retreated into disciplined seclusion (reading the sports pages, roaming on youtube) to confirm my conviction that a large section of liberalism had become contorted by a reluctance to entertain reality. And also that this reluctance very often stemmed from guilt or, closely related, a fear of raising doubts about certain orthodoxies.

You only had to look at the responses when some contributor dared to question the liberal-left shibboleths (that America was evil, that multiculturalism created social cohesion, that crime was a simple function of poverty, and so on - you know the drill). Accusations of racism and fascism were instantly bandied about as though anyone who wanted to open up the debate was by definition a Nazi.

Of course, it's an absurd tactic but also a surprisingly effective one. Among guilt-ridden liberals it often only takes one shrill voice of unreason to silence the expression of rational sense. I'm sure I'm not the only one who has seen this work, for example, in union meetings where otherwise sane people allow themselves to be morally directed by some fantasist whose single aim is to bring about a general strike and the downfall of capitalism.

It's impossible to quantify how much dogma has been swallowed by guilty liberals down the years but I know I've silently consumed a hefty chunk myself. Better not question this or that received wisdom, it might seem right-wing. Thus some key liberal principles have slowly been subverted. Free speech, it turns out, comes at a cost than many liberals are unprepared to pay: witness the lame response to The Satanic Verses, Behzti and the Danish cartoons. Female equality, once a defining principle of liberalism, is now routinely discussed in terms of a cultural luxury. The issue of race appears to have become mired in anti-racist rhetoric and practice that often emphasises and maintains racial division. And gay rights are in danger of being filed under the heading of western decadence.

Naturally, if one ever attempts to draw attention to this phenomenon, one is accused of building straw men. In a way, Cif has put flesh on the straw, bringing these censorial voices out into the open, albeit under the protective cloak of anonymity. And I think this has been a healthy and demystifying development for liberal debate. When you're first called a Nazi for, say, objecting to the preaching of racial hatred by religious leaders, it's actually quite unsettling. You think: No, I'm opposed to the very concept of racial determination; No, I believe firmly in freedom of expression (in which people are free also to criticise what's expressed); No, I don't recall calling for concentration camps and gas chambers.

In other words, you take the insult seriously. But then you quickly learn to dismiss it for what it is: nonsense. My book, which takes the form of a polemical memoir, is essentially an invitation to the reader and liberals in general to dismiss nonsense and assert sense. It's a call to reconsider liberal values and to appreciate the extraordinary achievements and benefits of liberal democracy. And no, it's not an argument that liberal democracy should be imposed on authoritarian regimes by western military intervention. But it is an argument against inviting authoritarian ideology in through the back door in the west out of some misplaced sympathy for Third World extremists.

It also seeks to address the postmodern, relativist wing of liberalism, the kind of argument that sees exceptions to the rule as proof that the rule doesn't apply. It's the mentality that focuses on the flaws in liberal democracy (of which there are obviously plenty) less to improve liberal democracy than to show that it's no better than any other system and quite possibly worse. Thus could the relativists argue that holding a dozen foreign terrorist suspects in Belmarsh under conditions of judicial review made Britain no different to a police state.

There are countless examples of this kind of thinking. It's essential, of course, that we remain vigilant to the threat to civil liberties from the state. Liberals know how to do this. What we've not really got the hang of is addressing the threats from elsewhere. It's the contention of the book that pretending they're not there, or dressing them up as resistance to oppression, won't make them go away.

Extracts from The Fallout, serialised in today's Observer, can be read here: Part 1Part 2Part 3.

A series of responses to the book will run next week on Comment is free.